Drop molten glass into cold water, and the resulting object has some peculiar properties. The glass hardens into a tadpole-shaped blob with an immensely tough bulb, as in tough enough to survive a blow from a hammer without a dent. Nick the fragile tail, though, and a chain reaction explosively disassembles the glass in a matter of milliseconds. Such objects are called Prince Rupert's drops or Dutch tears, and you can read more about them at the Wikipedia link or just watching this exciting but sometimes-corny video from SmarterEveryDay instead:
The choice to goggle up turned out to be very wise on close examination of the high-speed video. It's startling how explosively the drop comes apart when the tail is disturbed. This isn't playing fast and loose with the language, by the way. The fracture front shoots through the drop at sonic speed, releasing a substantial amount of stored energy that disperses into the surrounding air on a supersonic shock front. This is a rigorous textbook definition of the word "explosion," in this case driven by internal stress in the glass.
There's more to materials science than strength. Many glasses have tremendously high strength, but very little toughness, meaning that they can be pulled on more than most metals before breaking, but can't handle impacts very well. This is why glass is never used as a structural material without the support of a tough resin or metal matrix (as in fiberglass parts), while metals can stand a beating bare without much trouble. Except for the tail effect, Prince Rupert's drops seem both strong and tough, something very exciting even if you ignore the pretty high-speed videos of glass explosions.
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